1. Field of the Invention
This invention relates to a method and apparatus for forming an opening in the skin for the purpose of providing access to biological fluids for determining the concentration of analytes in the biological fluids.
2. Discussion of the Art
The prevalence of diabetes has been increasing markedly in the world. At this time, diagnosed diabetics represented about 3% of the population of the United States. It is believed that the total actual number of diabetics in the United States is over 16,000,000. Diabetes can lead to numerous complications, such as, for example, retinopathy, nephropathy, and neuropathy.
The most important factor for reducing diabetes-associated complications is the maintenance of an appropriate level of glucose in the blood stream. The maintenance of the appropriate level of glucose in the blood stream may prevent and even reverse many of the effects of diabetes.
Glucose monitoring devices of the prior art have operated on the principle of taking blood from an individual by a variety of methods, such as by needle or lancet. An individual then coats a paper strip carrying chemistry with the blood, and finally insert the blood-coated strip into a blood glucose meter for measurement of glucose concentration by determination of change in reflectance.
There are numerous devices currently available for diabetics to monitor the level of blood glucose. The best of these devices require the diabetic to prick a finger and to collect a drop of blood for placement on a strip, which is inserted into a monitor that determines the level of glucose in the blood. Pricking one""s finger tends to be painful. Moreover, a relatively large wound is produced by the pricking device, typically a lancet or a needle. It is known that the pain arising from the finger prick deters diabetics from compliance with the monitoring regimen. Lack of compliance increases the risk of complications due to diabetes. Thus there is a need for a more painless and less traumatic means of collecting biological samples for monitoring one""s level of glucose in blood.
Several patents have proposed that the level of glucose in blood can be monitored by measuring the level of glucose in interstitial fluid. In order to obtain samples of interstitial fluid, the barrier function of the stratum corneum must be overcome. Jacques, U.S. Pat. No. 4,775,361, discloses a method of ablating the stratum corneum of a region of the skin of a patient by using pulsed laser light of a wavelength, pulse length, pulse energy, pulse number, and pulse repetition rate sufficient to ablate the stratum corneum without significantly damaging the underlying epidermis. This patent discloses the use of laser light having a wavelength of 193 nm or 2940 nm. Laser light having wavelengths of 193 nm or 2940 nm can be provided by an excimer or Er:YAG light source, respectively, both of which are extremely expensive.
Tankovich, U.S. Pat. No. 5,423,803, discloses a process for the removal of superficial epidermal skin cells in the human skin. A contaminant having a high absorption in at least one wavelength of light is topically applied to the surface of the skin. Some of the contaminant is forced to infiltrate into spaces between superficial epidermal cells. The skin section is illuminated with short laser pulses at the above wave-length, with at least at least one of the pulses having sufficient energy to cause some of the particles to explode tearing off the superficial epidermal cells. In a preferred embodiment, the contaminant includes 1 micron graphite particles and the laser used in a Nd:YAG laser.
Zahrov, WO 94/09713, discloses a method for perforating skin comprising the steps of (a) focusing a laser beam in the shape of an ellipse at the surface of the skin with sufficient energy density to create a hole at least as deep as the keratin layer and at most as deep as the capillary layer; and (b) creating at least one hole, each hole having a width between 0.05 and 0.5 mm and a length of equal to or less than 2.5 mm. This patent discloses a variety of lasers suitable for carrying out this method. However, the method disclosed in Zahrov is limited to light source having a wavelength of 2940 nm. As stated previously, laser light of this wavelength can be provided by a Er:YAG light source, which is very expensive. Moreover, such a light source is relatively large, with the result that it would not be practical for use in a hand-held device.
In all of the methods involving forming an opening in the skin by means of a laser, a focused laser beam is used to form a small opening in the stratum corneum. A critical limitation of lasers in general is cost and power. The higher the power of a laser, the higher is its cost. If, in a desire to lower costs, a low power laser is used, the formation of an opening in the stratum corneum is preferably carried out by means of multiple light pulses. When multiple light pulses are used, it is desirable to cause each pulse, i.e., the first pulse and subsequent pulses, to strike the same area of the skin of the patient at the best focus, thereby increasing the efficiency of the application of light to the target, and minimizing the spreading of the light over a large area of the skin of the patient. However, because of random movement of the patient, it is difficult to maintain the focus of the laser at the best focus. Moreover, it is difficult to align the area to be struck by a given pulse with the area struck by a previously applied pulse.
It would be desirable to provide a method for providing an opening in the surface of the skin wherein an inexpensive light source is utilized, but wherein sufficient power is delivered within a short period of time. Thus, there is a need to focus, align, or both focus and align the laser between pulses to allow rapid and efficient opening of a region of the stratum corneum.
This invention provides methods and apparatus for focusing, aligning, or both focusing and aligning pulsed light on the surface of the skin of a patient. When the light is focused and aligned, the light can be used to form an opening, or pore, in the skin of the patient, from which opening or pore biological fluid can be obtained.
In one aspect, the invention involves a method for focusing light on a surface of skin of a patient. In general, the method for focusing light comprises the steps of:
(1) projecting at least one pulse of light, preferably driven at a level of energy that is insufficient to form an opening in the skin of the patient, onto the surface of the skin of the patient;
(2) collecting at least a portion of the light that is reflected from the skin of the patient;
(3) projecting the collected, reflected light onto a detector to provide a signal; and
(4) adjusting the projection of the pulsed light onto the surface of the skin of the patient in such a manner that the signal projected onto the detector is optimized.
When the pulsed light is properly focused, i.e., when it is characterized by the best focus, it can be used to provide energy to form an opening in the skin of the patient.
A preferred embodiment of a method for focusing light comprises the steps of:
(1) causing a pulsed beam of light, preferably driven at a level of energy that is insufficient to form an opening in the skin of the patient, to pass through a lens to project a spot on the surface of the skin of the patient;
(2) causing light that is reflected from the surface of the skin of the patient to pass through a lens to project a spot on a target on a detector; and
(3) moving the lens that projected the spot on the surface of the skin of the patient in such a direction that the quantity of the light reflected from the surface of the skin of the patient and projected on the target on the detector indicates the best focus.
After the lens is moved, a pulsed beam of light, driven at a level of energy at which an opening in the skin can be formed, can be caused to pass through the lens to project a spot on the surface of the skin of the patient, whereby formation of an opening in the skin occurs.
In another preferred embodiment, the invention involves a method for focusing light comprising the steps of:
(1) providing a pulsed beam of collimated light, preferably driven at a level of energy that is insufficient to form an opening in the skin of the patient;
(2) allowing a majority of the light from the beam to be reflected off the surface of a semi-silvered mirror to be transmitted through a lens to a region of the surface of the skin of the patient, from which region a portion of the light of the transmitted beam is reflected, passes through the semi-silvered mirror, then passes through a lens to project a spot on a detector having a central detection zone and a peripheral detection zone surrounding the central detection zone; and
(3) adjusting the lens that projected the spot on the surface of the skin of the patient so that the quantity of the light striking the central detection zone and the quantity of light striking the peripheral detection zone indicates the best focus.
After the lens is adjusted, a pulsed beam of light, driven at a level at which formation of an opening in the skin can occur, can be caused to pass through the lens to project a spot on the surface of the skin of the patient, whereby formation of an opening in the skin occurs.
As an alternative to the use of a semi-silvered mirror, a dichroic filter can be used to direct light to the skin from the light source and from the skin to the detector.
In another aspect, the invention involves a method for focusing and aligning light on a surface of skin of a patient. When more than one pulse of light is required to form an opening in the skin of the patient, aligning the light prior to each pulse will improve the efficiency of formation of the opening. In general, the method for aligning and focusing is the same as the method for focusing, with the difference being that aligning further includes a step for moving the spot of light formed by the source of light so that light strikes the surface of the skin at or near the position on the surface of the skin of the patient at which the previous spot of light struck the skin. In general, the method for focusing and aligning light comprises the steps of:
(1) projecting at least one pulse of light, preferably driven at a level of energy that is insufficient to form an opening in the skin of the patient, onto the surface of the skin of the patient;
(2) collecting at least a portion of the light that is reflected from the skin of the patient;
(3) projecting the collected, reflected light onto a detector to provide a signal; and
(4) adjusting the projection of the pulsed light onto the surface of the skin of the patient in such a manner that the signal projected onto the detector is optimized.
When the pulsed light is properly focused and aligned, e.g., when it is characterized by the best focus and best alignment, it can be used to provide energy to form an opening in the skin of the patient.
A preferred embodiment of the method for focusing and aligning light comprises the steps of:
(1) causing a pulsed beam of light, preferably driven at a level of energy that is insufficient to form an opening in the skin of the patient, to pass through a lens to project a spot on the surface of the skin of the patient;
(2) causing light that is reflected from the surface of the skin of the patient to pass through a lens to project a spot on a target on a detector;
(3) moving the lens that projected the spot on the surface of the skin of the patient in such a direction that the quantity of the light reflected from the surface of the skin of the patient and projected on the target on the detector indicates the best alignment;
(4) moving the lens that projected the spot on the surface of the skin of the patient axially in such a direction that the quantity of the light reflected from the surface of the skin of the patient and projected on the target on the detector indicates the best focus.
After the lens is adjusted, a pulsed beam of light driven at a level at which formation of an opening in the skin can occur is caused to pass through the lens to project a spot on the surface of the skin of the patient, whereby formation of an opening in the skin occurs. Then steps (1), (2), (3), (4) and the opening-forming step can be repeated until the opening formed in the skin is of the desired size.
In another preferred embodiment, the invention involves a method for focusing and aligning light comprising the steps of:
(1) providing a pulsed beam of light, preferably driven at a level of energy insufficient to form an opening in the skin of the patient, to pass through a lens to project a spot on the surface of the skin of a patient;
(2) allowing a majority of the beam to pass through a semi-silvered mirror to be transmitted through a lens to a region of the surface of the skin of a patient, from which region a portion of the light of the transmitted beam is reflected, passes through the semi-silvered mirror, then passes through a lens to project a spot on a detector having a central detection zone and a peripheral detection zone surrounding the central detection zone, the peripheral detection zone preferably divided into segments; and
(3) adjusting the lens that projected the spot on the surface of the skin of the patient so that the quantity of the light striking the central detection zone and the quantity of light striking the peripheral detection zone indicates the best alignment; and
(4) adjusting the lens that projected the spot on the surface of the skin of the patient so that the quantity of the light striking the central detection zone and the quantity of light striking the peripheral detection zone indicates the best focus.
After the lens is adjusted, a pulsed beam of light driven at a level at which formation of an opening in the skin can occur is caused to pass through the lens to project a spot on the surface of the skin of the patient, whereby formation of an opening in the skin occurs. Then steps (1), (2), (3), (4) and the opening-forming step can be repeated until the opening formed in the skin is of the desired size.
As an alternative to the use of a semi-silvered mirror, a dichroic filter can be used to direct light to the skin from the light source and from the skin to the detector.
In another aspect, this invention involves a method for aligning light on the surface of the skin of a patient, which method comprises the steps of:
(1) projecting at least one pulse of light onto the surface of the skin of the patient;
(2) collecting at least a portion of the light that is reflected from the skin of the patient;
(3) projecting the collected, reflected light onto a detector to provide a signal;
(4) adjusting the projection of the pulsed light onto the surface of the skin of the patient in such a manner that the signal projected onto the detector is optimized.
When the pulsed light is properly aligned, e.g., when it is characterized by the best alignment, it can be used to provide energy to form an opening in the skin of the patient.
In a preferred embodiment, the invention involves a method for aligning light on the surface of the skin of a patient comprising the steps of:
(1) causing a pulsed beam of light to pass through a lens to project a spot on the surface of the skin of a patient;
(2) causing light that is reflected from the surface of the skin to pass through a lens to project a spot on a target on a detector; and
(3) moving the lens that projected the spot on the surface of the skin of the patient in such a direction that the quantity of the light reflected from the surface of the skin of the patient and projected on the target on the detector indicates the best alignment.
In a preferred embodiment, the invention involves a method for forming an opening in the surface of the skin of a patient comprising the steps of:
(1) causing a pulsed beam of light, driven at a level of energy that is insufficient to form an opening in the skin of the patient, to pass through a lens to project a spot on the surface of the skin of the patient;
(2) causing light that is reflected from the surface of the skin to pass through a lens to project a spot on a target on a detector;
(3) moving the lens that projected a spot on the surface of the skin of a patient in such a direction that the quantity of the light reflected from the surface of the skin of the patient and projected on the target on the surface of the detector indicates the best alignment; and
(4) causing a beam of light, driven at a level of energy at which an opening in the skin can be formed, to pass through a lens to project a spot on the surface of the skin of the patient, whereby formation of an opening in the skin occurs.
After the lens is adjusted, a pulsed beam of light driven at a level at which formation of an opening in the skin can occur is caused to pass through the lens to project a spot on the surface of the skin of the patient, whereby formation of an opening in the skin occurs. Then steps (1), (2), (3), (4) and the opening-forming step can be repeated until the opening formed in the skin is of the desired size.
The use of the method of this invention eliminates the need for two sources of light, namely a first source of light for focusing or aligning or focusing and aligning the light that forms the opening and a second source of light for forming an opening in the skin. The same source of light used for focusing or aligning the opening-forming light can be used for forming an opening in the skin. By using the same source of light for focusing and aligning and for forming an opening in the skin, the errors that typically arise when using a focusing light separate from the opening-forming light are reduced.
In another aspect, the invention involves an apparatus suitable for focusing and aligning light. In general, the apparatus-comprises (a) a source of pulsed light, (b) a means for projecting pulsed light onto the surface of the skin of a patient, (c) a means for adjusting for alignment and focus of the pulsed light, and (d) a means for collecting light reflected from the surface of the skin and projecting the collected, reflected light onto a detector to determine the adjustment required for best alignment and best focus.
In a preferred embodiment, the apparatus comprises:
(a) a source of pulsed light, capable of being driven at a level of energy at which formation of an opening in the skin cannot occur;
(b) a lens for collimating light from said source of pulsed light;
(c) a mirror for reflecting a majority of the collimated light or a dichroic filter for transmitting a majority of the collimated light;
(d) a lens for focusing light reflected from the mirror or transmitted from the filter onto a region of the surface of the skin of a patient;
(e) a lens for focusing light reflected from the region of the skin onto a detector.
The detector is preferably the type of detector that has a central detection zone surrounded by a peripheral detection zone.
The foregoing apparatus may further include a mechanism for moving the focusing/alignment lens when the detector indicates that movement would reduce the distance between the spots on the skin struck by successive pulses of light. Alternatively, other means for adjusting the focusing and alignment or both include, but are not limited to, mechanisms for moving the entire apparatus, mechanisms for moving the source of light, mechanisms for moving the lenses, and the like.
The invention makes it possible to minimize the number of pulses of light needed to form an opening in the surface of the skin of a patient. Alternatively, the invention makes it possible to cause a given pulse of light to strike the skin at a position different from that struck by a previous pulse of light.